1. Field of the Invention
The present invention relates to radio frequency identification (RFID) systems. More particularly, the invention relates to a tag containing an RFID transponder having an antenna that can be easily tuned for use throughout the world in accordance with any national or regional standards.
2. Description of Related Art
Radio frequency transponders are used in many applications. In the automatic data identification industry, the use of RFID transponders (also known as RFID tags) has grown in prominence as a way to obtain data regarding an object onto which an RFID tag is affixed. An RFID tag generally includes a memory in which information may be stored. An interrogator containing a transmitter-receiver unit is used to query an RF tag that may be at a distance from the interrogator and moving relative to the interrogator. The RFID tag detects the interrogating signal and transmits a response signal containing encoded data back to the interrogator. Such RFID tags may have a memory capacity of several kilobytes or more, which is substantially greater than the maximum amount of data that may be contained in a bar code symbol or other types of human-readable indicia. Further, the RFID tag memory may be re-written with new or additional data, which would not be possible with a printed bar code symbol. RFID tags may also be readable at a distance without requiring a direct line-of-sight view by the interrogator, unlike bar code symbols or other types of human-readable indicia that must be within a direct line-of-sight and which may be rendered entirely unreadable if obscured or damaged. The RFID tags may either extract their power from the RF interrogating field provided by the interrogator, or may include their own internal power source (e.g., battery).
More particularly, an RFID tag includes a semiconductor chip containing RF circuitry, control logic, and memory. The semiconductor chip may be mounted on a substrate that also includes an antenna. In some applications, RFID tags are manufactured by mounting the individual elements to a circuit card made of epoxy-fiberglass composition or ceramic. The antennas are generally sections of wire (e.g., loops) soldered to the circuit card or consist of metal etched or plated onto the circuit card. The whole assembly may be encapsulated, such as by enclosing the circuit card in a plastic box or molded into a three dimensional plastic package. Recently, thin flexible substrates such as polyamide have been used to reduce the size of the RFID tag in order to increase the number and type of applications to which they may be utilized.
For commercial applications, such as pallet and container tracking, and truck and trailer tracking in shipping yards, it is known to utilize RFID tags that are tuned for communication in the ultra-high frequency (UHF) band (868 MHz-928 MHz). The UHF band represents a reasonable compromise between antenna size and transmitting range. Since the size of the antenna becomes smaller as the transmitting frequency increases, an RFID antenna suitable for UHF communications becomes small enough to be included in a conventional size shipping label. But, a drawback of using the UHF RFID tags is that there isn't one single global standard for UHF communications. In North America, UHF can be used unlicensed for 908-928 MHz, but restrictions exist for transmission power. In Europe, UHF is under consideration for 865.6-867.6 MHz. Its usage is unlicensed for 869.40-869.65 MHz only, but restrictions exist for transmission power. The North-American UHF standard (908-928 MHz) is not accepted in France as it interferes with its military bandwidths. For China and Japan, there is no regulation for the use of UHF, but each application for UHF in these countries requires a site license, which needs to be applied for at the local authorities and can be revoked. For Australia and New Zealand, 918-926 MHz is available for unlicensed use, but restrictions exist for transmission power. Thus, RFID tags communicating in the UHF spectrum must be specifically tuned for each regional/national application, and there is no single UHF RFID tag available for global use.
Accordingly, it would be very desirable to provide an RF tag that can be tuned for use under any national or regional standards.